RC lipo batteries vs 18650 battery safety?

[sonnetg]

Hello,
I am curious about the safety factor of lithium cells. I am a noob when it comes to lithium batteries. As far as I understand, both RC lipo batteries and 18650 batteries are lithium based, correct? RC Lipo pouch based batteries are lithium polymer and 18650 batteries are lithium cobalt? I am not sure on IMR and ICR type 18650 batteries though (Lithium manganese/lithium cobalt?). It seems IMR type has a safer chemistry.

I have been watching some youtube videos, and have come to the conclusion that lithium polymer based batteries can be extremely dangerous if not handled correctly. I have even seen few videos where a puffed Lipo battery caused a huge amount of smoke when punctured with a sharp object. On the other hand, I have a watched a video on ypedal channel where one 18650 batteries was sheared with a hacksaw, yet there wasn't a even a puff or smoke. Are 18650 batteries really this much safer than RC lipo packs?

Here's the video: https://www.youtube.com/watch?v=pwsuXKxzBKI


I know 18650 has metal casing and a safety valve to release the gas, but I had no idea that these batteries could be hacked and not go up in flames. That is pretty impressive. So does 18650 batteries have a different chemistry inside than most RC lipo batteries?

Any links to battery safety would be really helpful. I would really like to learn more on battery technology and safety before I build an ebike.

Thank you all so much,

 

[sonnetg]

Ok. I did some googling on various types of on IMR/IFR & ICR 18650 lion batteries, and found out the following info:

IMR -> LiCoO2 [Lithium Cobalt]
ICR -> LiMn [Lithium Manganese]
IFR -> LifePo4 [Lithium Phosphate]


So what exactly is Lipo chemistry based on? And what makes it so dangerous?

 

[sonnetg]

Found an interesting topic on this: http://www.rctech.net/forum/electric-road/182219-understanding-lipo-fires-101-a.html

It also seems most of the "big" 18650 li-ion manufacturers extensively stress test the cells in extreme environments, such as external shorting, heate test, overcharge, reverse charge, drop test, etc..

Here's a test data sheet from Sumsung after stress testing the cells.

http://www.batteryonestop.com/baotongusa/products/datasheets/li-ion/Samsung-SDI-ICR18650-26A.pdf

While RC Lipo batteries are also the same chemistry (LiCoO2 ), the manufactures obviously cut corners when it comes to safety and testing. I think I know which route to take...i will stick with 18650 for my ebike 8)

Samsung 18650 Safety Specification:

8.1 Drop Test :
Test method: Cell(as of shipment or full charged) drop onto the oak-board
Criteria: No leakage
8.2 Vibration Test
Test method: Cell(as of shipment) is vibrated along 2 mutually perpendicular axes with total excursion of 1.6mm and with frequency cycling between 10Hz and 55Hz by 1Hz/min.
Criteria: No leakage
9.1 Overcharge Test
Test method: To charge the standard charged cell with 12V and 2.6A at 25°C for 2.5 hours.
Criteria: No fire, and no explosion.
9.2 External Short-circuit Test
Test method: To short-circuit the standard charged cell by connecting positive and negative terminal by less than 50m wire for 3hours.
Criteria: No fire, and no explosion.
9.3 Reverse Charge Test
Test method: To charge the standard charged cell with charge current 2.6A By –12V for 2.5 hours.
Criteria: No fire, and no explosion

 

[dnmun]

lipo is not dangerous. it just has a low temperature at which it will go into thermal runaway than does lifepo4. you have to be negligent at many levels to have lipo fires and the most common is shorts in the balancing wires it now appears.

i had always thought that the term lipo, lithium polymer, meant that the cobalt oxide used for the cathodic matrix was spread out on a bed of some polymeric substance that would hold it together as the cathodic matrix swelled and shrank in size with the state of charge. i was abused of this opinion by mr luke but i still do not know why the term polymer was introduced to describe cells that use cobalt oxide as the cathodic material. or why it does not describe the other lithium chemistries using manganese or nickel cobalt aluminum also.

but lifepo4 will go into thermal runaway and can catch on fire also but it requires a much higher temperature during adiabatic heating than does the lipo. also the oxygen is held in a chemical bond to the phosphorus that does not give up the oxygen to flames until the temperature exceeds 600oC. which is hotter than the temperature of thermal runaway.

 

[sonnetg]

lipo is not dangerous. it just has a low temperature at which it will go into thermal runaway than does lifepo4. you have to be negligent at many levels to have lipo fires and the most common is shorts in the balancing wires it now appears.

i had always thought that the term lipo, lithium polymer, meant that the cobalt oxide used for the cathodic matrix was spread out on a bed of some polymeric substance that would hold it together as the cathodic matrix swelled and shrank in size with the state of charge. i was abused of this opinion by mr luke but i still do not know why the term polymer was introduced to describe cells that use cobalt oxide as the cathodic material. or why it does not describe the other lithium chemistries using manganese or nickel cobalt aluminum also.

but lifepo4 will go into thermal runaway and can catch on fire also but it requires a much higher temperature during adiabatic heating than does the lipo. also the oxygen is held in a chemical bond to the phosphorus that does not give up the oxygen to flames until the temperature exceeds 600oC. which is hotter than the temperature of thermal runaway.

i haven't found a whole lot of data sheet on lipo batteries. Lipos are everywhere around us. On cell phones, tablets, mobile devices, EVs and even light aircraft's. The generic term li-ion seem to apply for lithium polymer as well. Most of the fire incidents i see on ES and youtube seems to stem from user negligence and abuse. That being said, the pouch lipos would be no match compared to cylindrical shell 18650 batteries in terms of abuse and stress. You do have an interesting point on the cathode material inside lipos. I will see if I can find that info.

EDIT: I found this interesting article on BU: http://batteryuniversity.com/learn/article/the_li_polymer_battery_substance_or_hype

It seems the main difference between lipoly and 18650 is the Electrolyte separator.

quote from the site:

Both systems use identical cathode and anode material and contain a similar amount of electrolyte.

Li-polymer is unique in that a micro porous electrolyte replaces the traditional porous separator. Li-polymer offers slightly higher specific energy and can be made thinner than conventional Li-ion, but the manufacturing cost is said to be higher than cylindrical design. For purpose of discussion, pouch cells are often identified as being Li-polymer.

Are there any big brand names for lipo cells? I wonder if they would provide the test or safety available on the public domain

 

[sonnetg]

Found a Datasheet from A123 Systems. It seems these batteries have a very safe chemistry, based on nano phosphate, but these are not cheap by any means.

 

[dogman dan]

The thing about RC batteries is that the manufacturing of them is cheap and shoddy. That's how they make them so cheap.

IMO, once they puff they get more dangerous. Mostly because they get more vulnerable to letting out a flammable gas. Sometimes contaminants make them puff right away, other times they just puff slightly after quite a bit of use.

The best way to start an RC lipo fire is making some kind of mistake. Let a pack rattle around in a bag, box or basket, getting it's corners crushed, or other dings is one. Dropping the battery can ruin it, crushing pouches corners. Bottom line, pouches need protection. The shrink wrap is not enough. I heard of a lifepo4 pack burning a vespa because of damage rubbing against a sharp metal edge. (that one more likely a dead short problem) In another case, a battery rattling around loose in a bike basket got damage an burst into flames.

Another is if you have to take the battery apart to charge, then connecting back up in series, you make a mistake and connect a batteries + to -. Similarly, damage to balance wires could short one out. A dead short is always bad. In 1977 my truck burned because a 12v battery under the hood dead shorted. There is no "safe" battery for a dead short.

Then there is overcharging. If a lipo pack gets enough out of balance, a bulk charger can overcharge it causing a thermal runaway. RC lipo should never be stored or charged in a place you would not build a fire.

Over discharging is also not good. I Know of one fire where an over discharged pack was recovered, then later near the end of a discharge, it caught fire. Get rid of packs you know are damaged, whether by discharge or by dinging them.

"Safe" batteries still should not be treated carelessly. You don't set the battery and charger on your carpet right under the curtains, and start charging. Use some common sense.

Obviously an 18650 pack is less vulnerable to damage than pouch cells that are easily dinged or crushed at the corner. But you still have to consider the possibility of a dead short. Cheap packs may not have much protection from cells chafing on each other, or nickel straps chafing down through the shrink covers to short the pack. So even with 18650 packs, you should not treat them roughly, not letting them be dropped or rattle around too much in the battery box.

 

[Syonyk]

Found a Datasheet from A123 Systems. It seems these batteries have a very safe chemistry, based on nano phosphate, but these are not cheap by any means.

Cheap, Safe, Powerful. Pick two.

Hobby Lipos are what you get when you focus on cheap and powerful at all costs.

 

[Hillhater]

Remember, RC LiPo is 10+ year old technology, and at the time was the best option for very light weight battery packs for flying RC aircraft.
Even now, they remain the best for power density as required for performance heli or drone flyers. You cannot get a 18650 pack of similar weight to give the high currents (50+ C rates) needed.
The trade off is short cycle life and potential for fire.
RC LiPo was never designed for Ebike use, and is not recommended for anyone who is not familiar with the risks.

 

[dogman dan]

All true. A current generation 20 ah 18650 nmc or whatever pack can handle 30 amps fine, even with the cheapo cells. And 48v 20 ah is still relatively small and light.

So only if you need 40 amps out of 5 ah, or need 80 amps, do you really need RC packs. I tossed out about $1000 worth of very old Hobby King packs last week, and the last 20 ah of it will be gone next fall.

No plans to buy more at this point. Another 18650 pack with best quality cells would be nice, but for now, I can handle riding with only 30 amps, if it saves me the worry about burning down the house.